There is an increasing industrial and societal need for the preparation of ingredients that reduce or eliminate organic solvents and irritants, employ reagents that are themselves biocompatible and that optimally use starting materials derived from a natural source or are “nature-equivalent.” This is of urgent interest in consumer-facing industries such as personal and household care. One class of materials that might be approached in a “greener” manner is surfactants. In particular, there is a need for new betaines that are made in a more environmentally-friendly manner. Betaines are zwitterionic surfactants used in the personal care, household care, and other industries. They are classified as specialty co-surfactants that complement the performance of the primary surfactants. These co-surfactants also increase the mildness of the formulation by reducing irritation associated with purely ionic surfactants.
Betaines are commonly produced by a multi-step process based on coconut or palm kernel oil. For example, one process for the preparation of a prototypical betaine, fatty acid amidopropyl betaine, involves the amidation of fatty acids with 3-dimethylaminopropylamine (DMAPA) at high temperatures (150-175° C.). The intermediate fatty aminoamide is then reacted with sodium chloroacetate to afford the final product. The amidation requires high temperatures for conversion and distillation to remove unreacted starting materials. These high reaction temperatures can generate by-products and impart color to the products, requiring additional steps to remove the by-products and the color. DMAPA is also a known sensitizer and is found in trace quantities in the final formulation. Thus, betaines prepared under mild conditions without the use of DMAPA would be of great interest.
It would be highly desirable for the production of the betaines to occur under mild conditions and in high yield. Such a process would take place at lower temperatures, with fewer processing steps and by-products and it would lessen environmental impacts. These objectives can be met, for example, by the transesterification process disclosed below, beginning with the first step of converting the fatty acid to its methyl ester. It would further be highly desirable for the production of the betaines to occur directly from the fatty acids, avoiding a process step and eliminating the use of an alcohol such as methanol and its required recycle.